Film composite for electrostatic recording

ABSTRACT

A multilayer polymeric film composite for use in the electrostatic recording process is disclosed. The film composite comprises an image receptive layer having a surface abrasivity of about 0.015 inch to about 0.085 inch and a surface .Iadd.Sheffield .Iaddend.roughness of about 30 to about 180 .[.cc of air/minute.]. (.Iadd.Sheffield Units).Iaddend., an electronically conductive layer and a supporting layer. A transport assisting layer can be coated on the side opposite to the imaging side to give a four layer film composite which provides the required friction and surface roughness to allow the film to be driven smoothly through the printing equipment. Control of the abrasivity and surface roughness of the image receptive layer is used to obtain excellent image quality. The film composite provides high image quality over a wide range of humidities and archival properties.

BACKGROUND AND FIELD OF THE INVENTION

The present invention relates to a multilayer film composite for use inelectrostatic or electrographic recording. This recording process is animportant electronic non-impact printing technology which is now in wideuse as a means for achieving both high speed recording and high qualityimages. Electrostatic printers or plotters are useful as output devicesin computer-aided design, seismic recording, architectural design, andprinted circuit design, among others.

Electrostatic recording is the process of producing an image in the formof an electrostatic charge pattern on a dielectric surface andsubsequently developing that latent image by toning with oppositelycharged black or colored powder, usually colloidally suspended in aninsulating liquid.

In a typical writing or imaging process, a writing head, which containstwo or more rows of densely spaced styli and a backplate or frontplateelectrode, is selectively programmed by the plotter logic to placeminute dot-spaced electrostatic charges in latent image form on therecording medium. This medium is designed to receive and hold anelectrostatic charge pattern. After the latent image is electronicallyplaced on the medium, the medium is exposed to a liquid toner. Black orcolored particles suspended in the toner vehicle adhere to the mediumonly where a previous electrostatic charge was placed. Excess toner isremoved from the medium by a vacuum channel or wiper bars and the mediumis then dried by forced air, thereby fixing the image to the medium.This electronically produced print is often referred to as a hardcopy.

The most commonly used hardcopy media are paper, vellum and film. Eachhas its special requirements, and each has its special construction ordesign. This invention pertains to film and film-like surfaces for theelectrostatic printing process.

Although various film recording media have been proposed for us withelectrostatic recording plotters or printers, none of them has satisfiedfully the substantial need in the art, particularly for theelectrostatic recording devices such as the Benson (Oce Graphics)plotter. Verstec VS 3000 Series, 7000 Series, 8500 Series and 8500-HRSeries plotters, CalComp 5700 and 5800 Series plotters and HP 7600Series plotters. In fact, there are many deficiencies in the knownproducts which have considerably limited their commercial utility.

The performance of conventional recording media is inherently moisturesensitive since the conductive layer of said media employs ionicmoieties such as sulphonated polystyrene and dimethyl diallyl ammoniumchloride. Thus, repeated images or lines (ghosting) and low density areobtained at humidities above 60% relative humidity (RH), and low imagedensity results at humidities below 30%. This places an undesirableconstraint on the operating environment. Water-soluble ionic moieties inthe conductive layer cause bond failure and a resultant image layerbreakup when the print is subjected to water. This water-sensitivitythus makes the conventional recording medium nonarchival.

Conventional recording media fail to provide fully satisfactory imagequality, even al normal humidity conditions, i.e. 40-50% RH. Three mainimage defects which often are experienced in electrostatic recording are(1) flare which is randomly occurring bursts or explosions in plotterlines due to abnormal electrostatic discharge, (2) image breakup ordropouts which are irregular portions of missing image and (3) glitcheswhich are irregular specks, zippers, or non-uniform images occurring insolid dark images due to irregularities in the dielectric surface of themedia. Zippers, which are a common defect, are small horizontal lineswhich resemble a zipper seen in many recording films and are due to anelectrical shorting of a stylus which causes loss of information acrossa small bank of multiplexed styli. While all three types of defects areundesirable, dropouts or image deletions are the most serious because ofsignificant loss of information.

Furthermore, conventional recording media cannot transport reliablythrough the plotter, which results in inaccurate image rendition. Thisfactor is very important where high accuracy plots are required such asin the aircraft industry. It is also important when multiple-colorregistration is required.

In spite of the many attempts that have been made to improve thequalities of the conventional recording media, none of the presentcommercial products is free from all these drawbacks.

The present inventors have discovered that a multi-layer compositecomprising an image-receptive layer having electrical, surface profileand abrasivity characteristics within specific ranges, an electronicallyconductive layer possessing conductivity within a specific range over awide range of ambient humidity, a supporting layer with high dimensionalstability, and the ability to adhere to the adjacent layers, and,optionally, a layer which assists transport of the film through anelectrostatic plotter can serve to overcome the above-mentioneddrawbacks and perform in a manner that is superior to the films known inthe art. This advance in the art results from finding that certaincombinations of materials impart structural, electrical, chemical andphysical properties to the resultant structure such that it is asuperior electrostatic recording medium.

It is known in the art that an electrostatic recording medium must havea dielectric layer and a conductive layer, each conventionally defined,and, if neither provides the overall structural characteristics needed,a support layer. However, it also is known that this structure itselfdoes not provide a good electrostatic recording medium. There is a majorcommercial need for a medium which not only satisfies this minimumrequirement but which functions well under actual conditions ofcontinuous use in a variety of devices at a wide range of humidities toprovide an imaged product of high quality that can be used underpractical conditions and that can be exposed to water without loss ofarchivability. Although this need is well known and a great deal ofeffort has been devoted to research and development in the field, astructure which satisfies such quality requirements and which can beproduced economically has not been discovered previously. The balance ofdesirable properties achieved by certain structures against theconsequent loss in other desirable properties has led to repeatedfailure of entirely rational design efforts because there are manyrequirements and they were not thoroughly understood either individuallyor in combination.

As a result of these and similar factors the current state of the artrepresents failure to discover the range of materials, structures andmethods of producing them which can satisfy the clear need in the field.The present invention represents the discovery of such structures, theranges of materials from which they can be assembled and methods forproducing a high quality product.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a film compositewhich overcomes the above-mentioned drawbacks. This is attained by amultilayer film composite comprising (1) an image receptive layer, (2)an electronically conductive layer and (3) a supporting layer. Theinvention also provides a four layer film composite with good feedingproperties comprising (1) an image receptive layer, (2) anelectronically conductive layer, (3) a supporting layer and (4) atransport assisting layer.

The image receptive layer contains electrically resistive polymers andone or more types of particulates. The particulates are selected suchthat a balance in roughness and abrasivity is obtained. This balance isnecessary to ensure minimal drop outs, flares and toner wipe-off when aprint is made on an electrostatic plotter. The layer provides gooddielectric properties and electric chargeability suitable for holdingthe latent image charge pattern.

The electronically conductive layer used in the recording medium of thepresent invention comprises a metal oxide, a metal halide or a dopedform of one or more of these compounds dispersed in a polymer binder oralternatively an electronically conductive polymeric binder. Theconductivity of the layer is functionally independent of moisture. Thislayer is also water-insoluble. These two properties are essential forarchivability and for functionally stable and uniform electronicconductivity over a wide range of humidities. Almost no difference canbe seen in images made using the films of this invention at 10% to 85%RH. In contrast, little or no image would be obtained with filmscomprising ionically conductive layers at these extreme humidities. Infact, poor images are obtained even outside the range of 30 to 60% RHwith ionically conductive layers.

During coating of conventional dielectric films, drying of the coatingsolutions causes a loss of moisture from the conductive layer.Replacement of this moisture has to take place through the dielectriclayer. This process can cause small breakdown areas in this layer,resulting in the zipper defect previously described. In the presentinvention, no remoisturization of the conductive layer is necessary,thus eliminating one of the major causes of zippers. Further, theelimination of the humidification step simplifies the manufacturingprocess. The supporting layer is a polymeric material which has suitabledimensional stability, transparency or opacity, tensile strength,adhesion characteristics, thermal stability and hardness. Thissupporting layer may include an adhesion-promoting coating or pretreaton one or both sides of said layer. A number of base film supports areavailable that serve this purpose, the most common of which is polyesterfilm.

The transport-assisting layer comprises polymeric binders and pigments.This layer has good adhesion to the supporting layer and providessuitable friction and roughness characteristics to ensure that the filmcomposite transports reliably through the recording device,

In a preferred embodiment of the invention, the film composite iscomprised of an image receptive layer containing amorphous silica,crystalline silica and calcium carbonate particulates dispersed in apolymer matrix of polyvinyl butyral and polyacrylate, an electronicallyconductive layer containing a copolymer of methylmethacrylate-hydroxyethyl methacrylate and antimony doped tin oxideparticles, and a supporting layer of polyethylene terephthalate. Inanother preferred embodiment, the film composite also includes atransport assisting layer on the side opposite to the imaging side,containing silica particulates and polymeric binders comprisingmelamine-formaldehyde resin, partially hydrolyzed polyvinyl acetate, anda quaternary salt of an acrylamide copolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 shows a typical imaging system utilizing the recording medium ofthe present invention;

FIG. 2 shows a three component recording medium utilized in the presentinvention;

FIG. 3 shows a four component recording medium utilized in the presentinvention; and

FIG. 4 illustrates that abrasivity and surface roughness can beindependent parameters in a recording medium utilized in an imagingsystem.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, in a typical writing or imaging process, a writinghead 1, which can contain, for example, two rows of densely spaced styli2 and a segmented backplate electrode 3, is selectively programmed byplotter logic to place minute dot-spaced electronic charges in latentimage form on a recording medium 4. This medium is designed to receiveand hold an electrostatic charge pattern. After the latent image iselectronically placed on the recording medium, it is exposed to a tonermaterial 5, for example, a liquid toner. Black or colored particlessuspended in the toner vehicle adhere to the medium only where anelectrostatic charge was applied. Excess toner is removed from themedium by a vacuum channel or wiper bars and the medium is then dried byforced air, thereby fixing the image to the recording medium and formingthe hardcopy.

The film composite which is preferably used in the present inventioncomprises an image receptive layer 6, an electronically conductive layer7 and a supporting layer 8 (FIG. 2). A transport-assisting layer 9 canbe added on the side opposite to the imaging side to ensure reliablefeeding through the recording device (FIG. 3). The multilayerconfiguration of the present film composite ensures high image,qualities, archivability and good transport properties.

The image receptive layer of the present invention functions as a chargeretentive layer and a writing electrode-cleaning layer. The blend ofpolymers and particulates in the image receptive layer provides desiredsurface qualities which govern the image qualities. The surfacequalities are characterized by dielectric constant, dielectric strength,roughness, abrasivity, hardness and thermal characteristics. In order toovercome dropouts and provide low flare, it is necessary to balancesurface roughness and abrasivity of the image receptive layer. Dropoutscan be caused by a buildup of debris on the stylus head duringrecording. By providing film with a suitable abrasivity, it is possibleto prevent this buildup. Surface roughness is often confused withabrasivity, and it can be shown that a rough surface with low abrasivitywill still give image deletion due to dropouts. The recognition of thisimportant difference and the independent control of roughness andabrasivity contributes substantially to the improved quality of the filmof this invention.

The term abrasion is commonly used to refer to a process of wear inwhich there is displacement of material from a surface during relativemotion against hard particles or protuberances, whereas surfaceroughness refers to unevenness of the surface.

As is clear from FIG. 4, surface roughness and abrasion are parametersthat are not necessarily dependent on each other. In fact, in thisparticular example where a mixture of amorphous and crystalline silicasis employed, the surface .Iadd.Sheffield .Iaddend.roughness .[.(units ofcc air/minute).]. (.Iadd.Sheffield Units) .Iaddend.increases with anincrease in the percentage of amorphous silica, whereas the abrasion(units of inch) decreases due to a decrease in the crystalline silicacontent. Dropouts become worse as abrasivity is decreased. Flares, onthe other hand, become worse as the abrasivity is increased.Consequently, it is necessary to have the right blend of particulates toensure that a balance between roughness and abrasivity is obtained,giving a dropout-free recording with low flares. The technique formeasuring abrasivity is therefore important. A test method called the"Arkwright Abrasivity Tester" has been developed for this purpose whichis described later.

A measure of roughness is necessary to provide good electrical dischargeand subsequent toning of the film. The surface roughness also helps toprevent excess toner wipe-off of the image by the vacuum channel orother means used for removing excess toner from the film during thefinal stage of printing. Toner wipe-off of the image results in very lowimage density.

The image receptive layer determines the electrostatic charge acceptedby the film composite and the time duration over which it will hold thischarge. The polymers used for the image receptive layer should beelectrically resistive and stable. Suitable dielectric materials includethermoplastic polymers such as polyesters, polyvinyl chloride, polyvinylfluoride, nylon, polyvinyl acetate, cellulose acetate,acrylonitrile-butadiene-styrene polymers, polystyrene, polyurethanes,polyalkylacrylates, polyvinyl butyral and copolymers and blends thereof,and thermosetting polymers such as phenolic resins, melamine resins,epoxy resins and silicone resins. The dielectric constant (ASTM D150) ofthe polymer normally employed is in the range of about 1.5 to about 6.5measured at 25° C. and 1 KHz and preferably 1.5 to 4.5. A value ofdielectric constant below 1.5 imparts lower capacity to hold charge,thereby giving lower image density; whereas a value of dielectricconstant above 6.5 tends to cause storage of excessive charges, therebyresulting in deleterious background.

The polymer binders used in the image receptive layer must havesufficient dielectric strength to support the charging current withoutbreakdown. When breakdown does occur, a hole is actually burned in thelayer and a circle of low charge is formed around the point ofbreakdown. These areas manifest themselves as white untoned spotsnormally with a dark center dispersed in the print.

The optimal surface roughness and abrasivity of the image receptivelayer result from incorporating inorganic or polymeric particulates intothe polymer binders. Although the exact mechanism by which they operateis not clearly understood, it can be postulated that these particulatesare selected to serve several functions:

(1) The particulates function as a spacer which creates an ionizationair gap between the image receptive layer and the writing electrode. Fora given voltage, the Paschen curve defines the range of spacing betweenthe image receptive layer surface and the writing electrode. An imagereceptive layer which provides an air gap distance outside of this rangewill not perform adequately. Therefore, the combined effect of the sizeof the particulates and the surface shape must provide a suitable gap.The combined effect can be quantified by a Sheffield reading of thesurface roughness. The preferable average particulate size range isabout 2 to about 15 microns.

(2) The particulates provide desired surface profile. Generally, asurface profile that is too low produces image break-up. A surfaceprofile that is too high creates white-spotting (in solids andhalftones) and also image break-up. It has been discovered that asuitable surface profile results when the particulate materials employedare required to provide a surface roughness of from about 30 to about180 .[.cc of air/minute.]. (.Iadd.Sheffield Units) .Iaddend.as measuredon a Sheffield smoothness tester, preferably from 60 to 150 .[.cc ofair/minute.].. The surface profile characteristic depends on the type ofparticulates employed and their concentration in the polymer binders.

(3) The particulates also clean the writing electrode to prevent imagedropout. Due to the heat and other effects generated by discharge andfriction with the writing electrode, extraneous matter often depositsonto the electrode head. Accordingly, cleaning of the writing electrodeis usually necessary to prevent deterioration in recordingcharacteristics. This is achieved by employing particulates of specifiedabrasivity. The control of abrasivity of the image receptive layer isessential. Too low an abrasivity will not prevent image dropout and toohigh an abrasivity causes excessive flare. It has been demonstrated thata minimum value of 0.015 inch is needed to attain dropout freerecording, and that values above 0.085 inch result in excessive flarelevels. Preferably, the image receptive layer has a surface abrasivityof from 0.03 to 0.07 inch.

The abrasivity is measured on an Arkwright abrasivity tester. Theabrasivity testing device is a crockmeter (Model #CM1) obtained fromAtlas Electric Devices Company. First, the samples are cut into 8 1/2"by 11" pieces which are then humidified at 50% RH for one hour. A 3Hpencil lead of at least 1 inch long, but not longer than 1.2 inches, isplaced in a rubber holder in such a way that 3/16 inch of lead isextended beyond the rubber surface. The length of lead exposed ismeasured using a caliper. The rubber holder along with the lead isplaced in a hole on the underside of the arm of the crockmeter. Thepreconditioned sample is then put on an abrasive pad of the crockmeterand the counter is set at zero. The handle of the crockmeter is thenturned at a rate of approximately one revolution per second and thesample is simultaneously pulled with a slow, steady and straight backmotion. The process is continued until the counter reads fifty. Afterthis, the rubber holder with lead is removed from the arm of thecrockmeter. The length of lead is again measured using the same caliper.This value of length is subtracted from the original value of length.The resulting value is expressed as abrasion in units of an inch. Theabrasion value represents an average of five tests for each specimen.

Not all pigments are suitable to achieve the requisite abrasivity androughness parameters in the present invention. The pigments may not bedecomposed or fragmented by the imposed charge during the imagingprocess, nor cause electrical breakdown. Examples of inorganic orpolymeric particulates suitable for the image receptive layer includeamorphous silica, crystalline silica, alumina trihydrate, calciumcarbonate, clays, aluminum silicates, polyolefin particulates, organicpigments and mixtures thereof. Because of the importance of clear filmin many applications, it is necessary to keep a minimum haze, preferablyin the range of 10 to 45 percent, as measured on Gardner Pacific'sHazeguard XL211. Thus, it is important to select pigments that givemaximum clarity. Traditionally, on a paper medium, high concentrationsof amorphous pigment are used, but this leads to high haze, making itinappropriate for use on a clear film medium. The choice of pigments toprovide the balance of roughness and abrasivity is best determined byfirst measuring the abrasivity and roughness of the candidate pigmentsin the coating and then by selecting the most suitable to achieve theproper blend.

The particle size of the particulates is measured using a Malvernparticle size analyzer. The surface roughness is measured on a BendixPrecisionaire Sheffield Smoothness instrument. The roughness value ismeasured by raising the testing head and placing an 8 1/2"×11" sample onthe glass plate and then slowly lowering the testing head in a gentlemanner with no discernible impact due to downward motion of the head.The Sheffield roughness value can be obtained from the position of thefloat between red calibrating lines on the scale, once the float reachesa point of stability. The value is expressed as .[.cc of air/minute.]..Iadd.a Sheffield Unit.Iaddend.. The higher the value, the rougher isthe surface. The Sheffield roughness value represents an average of fivetests for each specimen.

An appropriate amount of the particulates added to the polymer bindersis within the range of about 5 wt% to 30 wt% and more preferably 15 wt%to 21 wt% by weight of particulate solids to polymer binders. Thecoating weight of the image receptive layer typically ranges from 1.5grams-per square meter to 12 grams-per square meter, more specificallyfrom 3 to 6 grams-per square meter.

The significant feature of the conductive layer in the present inventionis that its electrical characteristics are functionally independent ofmoisture. In the conventional recording media, the conductive layer isionically conductive which performs satisfactorily only in the presenceof certain amounts of moisture. Best results are obtained at about 50%RH. Poor image quality is obtained outside the range of 30-60% RH. Thecarrier of the charge in such a medium comprises ions which can conductcharge appropriately only in the presence of moisture. Due to inherentwater sensitivity of these ionic materials, a breakup in the image layeroccurs when the print is subjected to water, making it nonarchival.

However, unlike conventional recording media, the conductive layer usedin the present invention is electronically conductive. The dominantcarriers in such a medium are electrons or "holes" instead of ionicmoieties. Therefore, this type of layer contributes to archivability,functional stability and uniform electronic conductivity over a widerange of humidities. An important feature of the present invention isthat the electronically conductive layer can be coated by one of theconventional coating methods instead of using expensive processes suchas sputtering or vacuum deposition.

The electronically conductive layer contains at least one electronicallyconductive particulate in at least one polymer binder. Theelectronically conductive particulates that can be used in theelectronically conductive layer are doped metal oxides such as doped tinoxide, doped indium oxide and doped zinc oxide and metal-containingsemiconductors such as the metal halides Cu and AgI. Other suitableconductive particulates include those in which a nucleus such as TiO₂,SiO₂, ZnO or the like is covered by a conductive metal oxide such asantimony or fluorine doped tin oxide or the like. The electronicconductivity can also be achieved by using electronically conductivepolymers such as polyacetylene, poly p-phenylene, poly p-phenylenesulfide and polypyrrole in their conductive forms.

Metal oxides used in the present invention are semiconductors such asdoped tin oxide, indium oxide and zinc oxide. Among these metal oxides,doped tin oxide is found most suitable for use, from the viewpoint ofopacity, color, cost and stability of conductivity. The dopants whichcan be used for tin oxide and zinc oxide are antimony, indium,phosphorus and fluorine, and the dopants used for indium oxide areantimony, phosphorus and fluorine. The concentration of the dopantsusually is 0.5 to 20%. The doped metal oxide may be used on its own oron the surface of suitable clear, opaque or colored particulates.

When clear films are required, the conductive pigments should be of suchsize as to minimize light refraction. To have optimum transparency, theaverage particle size of the doped metal oxide should be about 0.2micron or less. Acceptable transparency may be obtained with a somewhatlarger particle size. If a white, opaque electronically conductive layeris desired, then it is also possible to use an electroconductive pigmentconsisting of a nucleus of TiO₂ with a chemical surface treatment ofdoped tin oxide.

In order to obtain a conductive layer with a surface resistivity rangingfrom about 1×10⁶ ohms/sq to 1×10⁸ ohms/sq at 25° C., the ratio of metaloxide to polymer binder should be about 5:1 to about 1:1, preferablyfrom about 3:1 to about 1.5:1. Some of the newer printer-plotters withno multiplexing can use conductive layers with a surface resistivitybelow about 1×10² ohms/sq. Thus, for such machines the lower resistivitylimit can be extended.

As the binder polymers for the electronically conductive layer,thermoplastic resins or thermosetting resins employed in conventionalcoatings, such as acrylic resins, vinyl acetate resins, vinyl chlorideresins, carbonate resins, protein binders, polyester resins, styreneresins and copolymers of said polymers can be suitably used. Polyesterresins and copolymers of methyl methacrylate and hydroxyethylmethacrylate (composition of 50:50 to 98:2) are most preferable from thestandpoint of providing a layer having excellent transparency and goodelectronic conductivity.

A preferred embodiment of the electronically conductive layer usingdoped tin oxide has a pigment to binder ratio of 3:1 to 1.5:1 and has acoating weight of 0.25 to 5.00 gm/sq meter. The resin used is acopolymer of methyl methacrylate and hydroxyethyl methacrylate. Thecoating weight of the conductive layer may vary greatly depending uponthe required conductive effect, required coating film strength, pigmentto binder ratio, and other requirements, but generally it is in therange of 0.5 gram-per square meter to 3 grams-per square meter.

The supporting layer of the present invention is a polymeric materialwhich has suitable dimensional stability, transparency or opacity,tensile strength, adhesion characteristics, thermal stability andhardness. Suitable polymeric materials for use as a supporting layer aretransparent or opaque thermoplastic polymers, including polyesters,polysulfones, cellulose acetate, polycarbonates, polystyrene,polyimides, polyolefins, poly(methyl methacrylate), cellulose esterssuch as cellulose acetate and others. A polyethylene terephthalatepolyester film is particularly preferred. The thickness of the layer isnot particularly restricted, but typically is in the range of about 2 to10 mils, preferably about 3.0 to about 5.0 mils. The supporting layermay be pretreated to enhance adhesion of the polymeric coating thereto.

The transport-assisting layer of the multi-layer film composite isplaced on the side opposite to the imaging side. This is done to provideappropriate friction and surface roughness to allow the film to bedriven through the recording device in a smooth fashion, that is,without slip-sticking. Without this layer, inconsistent film feedingoften occurs through the device and results in loss of dimensionalaccuracy.

The coefficients of static and dynamic friction of thetransport-assisting layer are measured against itself using an Instrontensile tester (Model #1120) in accordance with ASTM D1894-78. Thestatic friction refers to the resistance offered by the surface forinitiating the relative motion of an object under the influence ofexternal force, whereas the dynamic friction refers to the resistanceoffered by the surface to an object while the object is in motionrelative to the surface. The values of coefficient of static and dynamicfriction can be obtained from the recording output of the instrument.The first long spike on the chart is a measure of the coefficient ofstatic friction whereas the average of the remaining high peaks and lowpeaks is a measure of the coefficient of dynamic friction.

In addition to friction, the surface roughness also plays an importantrole in the smooth feeding of film through the printer. The transportassisting layer includes a small percentage of particulates which act asspacers. These spacers help to reduce the drag of the film through theelectrographic printer and thereby 55 ensure smoother feeding.

The coefficients of friction, the nature of the friction curve andsurface roughness of the transport assisting layer determine thetransport property. The phenomena of slip-stick refers to a stepwisemovement during film transport as contrasted with a continuous movementand is a function of the foregoing factors.

The coefficients of static and dynamic friction are, respectively, inthe range of 0.25 to 0.75 and 0.20 and 0.70 units. The averagepeak-to-valley distance of the dynamic peaks is preferably below 0.15unit. The Sheffield surface roughness of the transport assisting layeris in the range of 10 to 100 .[.cc of air/minute.]. .Iadd.SheffieldUnits .Iaddend.and preferably in the range of 15 to 65 .[.cc ofair/minute.]. .Iadd.Sheffield Units.Iaddend.. The appropriate frictionvalues, surface roughness and surface profile will ensure a continuous,smooth transport in contrast to a stepwise transport. It is the lack ofrecognition of the need for a controlled surface friction and roughnessthat is responsible for the poor performance of some products in themarket. Preferably, the transport assisting layer is made anti-static toavoid the development of spurious charges and to assist in smoothtransport through the plotter.

The clear transport-assisting layer contains polymer binders, inorganicor polymeric particulates, and/or conductive moieties. The ratio ofpolymer binder to particulates preferably should be about 100:1 to about166:1 by weight, but will function at a lower ratio but at a loss oftransparency. The transport-assisting layer has a surface resistivity ofabout 1×10⁶ to about 1×10¹³ ohms/sq at 25° C. and 50% RH.

The CAD, CAM industry often requires a matte finished medium on whichadditional manual drafting with pen and pencil can be done. This type ofmatte coating is well known in the art and consists of suitable inkreceptive resins, together with pigments which provide an abrasivesurface with enough tooth to produce pencil images. Because of itspigmented drafting surface, this type of matte coating is useful as atransport layer.

The polymers used as binders in the transport-assisting layer includeacrylic resins, vinyl acetate resins such as hydrolyzed polyvinylacetate, vinyl chloride resins, cellulose acetate bulyrate resins,cellulose acetate propionate resins, carbonate resins, polyester resins,urethane resins, epoxy resins, melamine-formaldehyde resins and styreneresins. Preferred polymer binders useful in the coating composition ofthe invention are melamine-formaldehyde resins and 15-75% hydrolyzedpolyvinyl acetate. The polymeric binder can be crosslinked using acidsas catalysts such as benzoic acid, p-toluene sulphonic acid, n-butylphosphoric acid, amine salts of carboxylic acids and alkyl sulphonicacids. The particulates that can be used in the transport assistinglayer include amorphous silica, crystalline silica, calcium carbonateand polyolefin, either singly or in combination.

The conductive property of the transport-assisting layer is introducedby doped metal oxides or ionic conductive polymers. Preferred examplesof conductive agents used in the invention include tin oxide doped withantimony, indium, phosphorus or fluorine, sulfonated polystyrene resin,quaternized cellulose ether, quaternized acrylics such as quaternarysalts of diacetone acrylamide copolymer resins, and the like.

When a clear film composite is desired, it is essential t disperse theelectronically conductive pigment in the conductive lacquer so as toobtain a transparent conductive coating. Dispersion of said pigment isalso required to obtain the requisite electrical conductivity.Dispersion refers to the complete process of incorporation of powderedpigments into the liquid medium so that the final product consists offine pigment particle distribution throughout the medium. Commerciallyavailable doped tin oxide is specified to have a particle size in therange of 0.02 to 0.10 micron. However, it is possible that theseparticles agglomerate during storage. It is therefore essential todisperse these types of pigments so as to deagglomerate the particles totheir original particle size. The submicron size particles can beobtained by dispersing the lacquer in dispersing equipment such as aball mill, sand mill, bead mill, or similar type of dispersingequipment.

The supporting layer is first coated with the electronically conductivecoating using the Meyer rod technique and dried in an air dried oven ata temperature range of 100° to 150° C. for about 4 minutes to 2 minutes.The image receptive layer is then applied over the conductive coatingusing the same techniques and dried at a temperature range of 80° to120° C. for about 2 minutes to 1 minute.

The transport-assisting layer may then be placed on the opposite side ofthe supporting layer using the Meyer rod technique and dried at atemperature range of 120° to 150° C. for 4 minutes to 2 minutes.

The multilayer film then can be striped on the image receptive layeralong the edges using conventional conductive black ink which is commonin the industry. This is needed to ground excess background chargeduring recording.

Any of a number of methods may be employed in the production coating ofthe individual layers in the film composite, such as roller coating,wire-bar coating, dip-coating, air-knife coating, slide coating, curtaincoating, doctor coating, flexographic coating, or gravure coating. Suchtechniques are well known in the art.

The film composite having a multi-layer configuration in accordance withthe present invention has unique surface and electrical characteristics.The present film composite features good image formation, archivability,reliable handling, and a minimum of image dropouts, zippers and flare.It performs well over a wide range of humidities.

The following examples are further illustrative of the present inventionbut are by no means limitative of the scope thereof.

EXAMPLE I

An electronically conductive lacquer of the following composition isprepared:

    ______________________________________                                        Copolymer of methyl methacrylate-                                                                     18.23  parts                                          hydroxyethyl methacrylate                                                     (Ratio 78:22)                                                                 Antimony doped tin oxide                                                                              11.48  parts                                          (8.6 percent antimony content)                                                Methyl ethyl ketone     63.90  parts                                          Methyl carbitol         6.39   parts                                          ______________________________________                                    

Antimony doped tin oxide is premixed with methyl ethyl ketone and methylcarbitol for 5 minutes. The copolymer of methylmethacrylate-hydroxyethyl methacrylate is then added to the premix andmixed for another 5 minutes. This premix is then dispersed usingdispersing equipment for one hour. The lacquer is then coated on a 4 milthick transparent polyethylene terephthalate film using a Meyer rod anddried in an air dried oven at 125° C. for 2 minutes. This gives atransparent conductive coating with a surface resistivity of about 2×10⁶ohms/square.

An image receptive layer of the following composition is then coated onthe electronically conductive layer.

    ______________________________________                                        Toluene                 40.04  parts                                          Methyl ethyl ketone     40.04  parts                                          Acrylic copolymer (55%) 8.65   parts                                          (DeSoto Incorporated)                                                         Amorphous silica        0.43   parts                                          (Av. particle size 8.4 microns)                                               Crystalline silica      0.65   parts                                          (Av. particle size 4.7 microns)                                               Calcium carbonate       1.43   parts                                          (Av. particle size 3.8 microns)                                               Polyvinyl butyral       8.76   parts                                          (Monsanto Company)                                                            ______________________________________                                    

The lacquer is made by mixing toluene, methyl ethyl ketone and theacrylic copolymer for 10 minutes. Amorphous silica, crystalline silica,calcium carbonate and polyvinyl butyral are then added and mixed for 30minutes under a high speed Cowles mixer.

The lacquer is applied to the previously coated film using a Meyer rodand dried at 90° C. for 2 minutes.

The transport assisting layer of the following composition can then becoated on the side opposite to the electronically conductive layer andimage receptive layer of polyethylene terephthalate film.

    ______________________________________                                        Methyl Cellosolve       36.92  parts                                          Methanol                38.89  parts                                          Quaternary salt of diacetone                                                                          3.53   parts                                          acrylamide copolymer                                                          (Calgon Corporation)                                                          35% Hydrolyzed polyvinyl acetate                                                                      11.92  parts                                          (35% vinyl alcohol and 74% vinyl                                              acetate)                                                                      Melamine-formaldehyde   6.59   parts                                          (Reichhold Chemicals Inc.)                                                    Amorphous silica        0.06   parts                                          (Av. particle size 8.4 microns)                                               Acid Catalyst           2.10   parts                                          ______________________________________                                    

The lacquer is prepared by mixing methyl cellosolve, methanol anddiacetone acrylamide copolymer for 5 minutes. To the solution, 35%hydrolyzed polyvinyl acetate, melamine-formaldehyde and amorphous silicaare added and mixed for another 20 minutes. The catalyst is then addedand mixed for 2 minutes. The lacquer is coated using a Meyer rod on theside opposite to the electronically conductive layer and image receptivelayer on the polyethylene terephthalate film and dried at 120° C. for 2minutes. The coated film is then striped with a conductive ink on theimage receptive layer of the film.

The coated film is printed on a Versatec V7436 electrostatic plotter.Excellent print density with a very low level of flare, no dropouts andno toner wipe off is obtained.

The haze level of this clear coated film is 36 percent. The Sheffieldsurface roughness and abrasivity of the coated film are 95 .[.cc ofair/minute.]. (.Iadd.Sheffield Units) .Iaddend.and 0.047 inch,respectively.

In contrast, a similar film is made with the only difference being thatthe image receptive layer does not contain any crystalline silica. Theamount of amorphous silica is increased to compensate for the absence ofcrystalline silica. The Sheffield roughness and abrasiveness of the filmare 120 .[.cc of air/minute.]. (.Iadd.Sheffield Units) .Iaddend.and0.002 inch, respectively. The haze level of the coated film is 40percent. When the film is printed on a V7436 electrostatic printer,severe dropout in the print is observed.

EXAMPLE II

Another electrographic film of the following composition is prepared inthe same manner as in Example I.

    ______________________________________                                        The image receptive layer                                                     Methyl ethyl ketone     38.66  parts                                          Toluene                 38.66  parts                                          Acrylic copolymer (55%) 8.77   parts                                          (DeSoto Incorporated)                                                         Amorphous silica        0.53   parts                                          (Av. particle size 8.4 microns)                                               Crystalline silica      2.10   parts                                          (Av. particle size 4.7 microns)                                               Polystyrene             5.64   parts                                          (Hercules Incorporated)                                                       Polyvinyl butyral       5.64   parts                                          (Monsanto Company)                                                            The electronically conductive layer                                           Toluene                 56.12  parts                                          Isopropyl alcohol       9.90   parts                                          Polyethylene terephthalate resin                                                                      6.32   parts                                          (Goodyear Tire & Rubber)                                                      Titanium dioxide, surface treated                                                                     27.66  parts                                          with antimony doped tin oxide                                                 (10 percent antimony content)                                                 The supporting layer                                                          White opaque polyethylene                                                     terephthalate                                                                 The transport-assisting layer                                                 Methyl Cellosolve       36.92  parts                                          Methanol                38.89  parts                                          Quaternary salt of diacetone                                                                          3.53   parts                                          acrylamide copolymer                                                          (Calgon Corporation)                                                          35% hydrolyzed polyvinyl acetate                                                                      11.92  parts                                          (35% vinyl alcohol and 75% vinyl                                              acetate)                                                                      Melamine-formaldehyde   6.59   parts                                          (Reichhold Chemicals Inc.)                                                    Amorphous silica        0.06   parts                                          (Av. particle size 8.4 microns)                                               Acid Catalyst           2.10   parts                                          ______________________________________                                    

This film has a Sheffield roughness of 130 .[.cc of air/minute.].(.Iadd.Sheffield Units) .Iaddend.and abrasiveness of 0.070 inch. Thefilm, when printed, has good print density and no dropouts.

EXAMPLE III

Another electrographic film is prepared in the same manner as in ExampleI using the following components:

    ______________________________________                                        The image receptive layer                                                     Toluene                 43.84  parts                                          Methyl ethyl ketone     43.84  parts                                          Polyvinyl butyral       10.56  parts                                          (Monsanto Company)                                                            Amorphous silica        0.35   parts                                          (Av. particle size 8.4 microns)                                               Crystalline silica      1.41   parts                                          (Av. particle size 4.7 microns)                                               The electronically conductive layer                                           Methyl ethyl ketone     65.48  parts                                          Copolymer of methyl methacrylate-                                                                     17.86  parts                                          hydroxyethyl methacrylate                                                     (Ratio 78:22)                                                                 Melamine-formaldehyde resin                                                                           1.86   parts                                          (American Cyanamid)                                                           Antimony doped tin oxide                                                                              14.88  parts                                          (8.6 percent antimony content)                                                parts                                                                         Copolymer of methyl methacrylate-                                                                     17.86  parts                                          hydroxyethyl methacrylate                                                     (Ratio 78:22)                                                                 Melamine-formaldehyde resin                                                                           1.86   parts                                          (American Cyanamid)                                                           Antimony doped tin oxide                                                                              14.88  parts                                          (8.6 percent antimony content)                                                The supporting layer                                                          Transparent polyethylene                                                      terephthalate                                                                 The transport-assisting layer                                                 Methyl Cellosolve       36.92  parts                                          Methanol                38.89  parts                                          Quaternary salt of diacetone                                                                          3.53   parts                                          acrylamide copolymer                                                          (Calgon Corporation)                                                          35% hydrolyzed polyvinyl acetate                                                                      11.92  parts                                          (35% vinyl alcohol and 75% vinyl                                              acetate)                                                                      Melamine-formaldehyde   6.59   parts                                          (Reichhold Chemicals Inc.)                                                    Amorphous silica        0.06   parts                                          (Av. particle size 8.4 microns)                                               Acid Catalyst           2.10   parts                                          ______________________________________                                    

The Sheffield roughness and the abrasivity are 113 .[.cc ofair/minute.]. (.Iadd.Sheffield Units) .Iaddend.and 0.065 inch,respectively. The haze level of the coated film is 33 percent. The film,when printed on a Versatec V7436 printer, gives good print density andno dropouts but with slightly more flares than Example I.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such modifications as would be obvious to oneskilled in the art are intended to be included within the scope of thefollowing claims.

We claim:
 1. A multi-layered polymeric film composite for use in anelectrostatic or electrographic recording process comprising:an imagereceptive layer having a surface abrasivity of 0.015 inch to 0.085 inch,a surface roughness of 30 to 180 .[.cc of air/minute/.]. .Iadd.SheffieldUnits; .Iaddend. an electronically conductive layer containing at leastone electronically conductive particulate in at least one polymerbinder; and a supporting layer, said image receptive layer beingdisposed on said electronically conductive layer which is, in turn,disposed on said supporting layer.
 2. A film composite according toclaim 1, further comprising a transport-assisting layer on the sideopposite to the imaging side of the film.
 3. A film composite accordingto claim 1, wherein the electronically conductive particulate is a dopedmetal oxide.
 4. A film composite according to claim 1, wherein theelectronically conductive particulate is a metal halide.
 5. A filmcomposite according to claim 1, wherein the electronically conductiveparticulate comprises a nucleus which is covered by a conductive metaloxide.
 6. A film composite according to claim 1, 2, 3, 4 or 5, whereinthe image receptive layer contains polymer binders and particulates, andpossesses a dielectric constant of 1.5 to 6.5 measured at 25° C. and 1KHz.
 7. The film composite according to claim 6, wherein said polymerbinders in the image receptive layer are selected from the groupconsisting of polystyrene, polyacrylates, polyvinyl butyral, polyvinylacetate, polyesters. acrylonitrile-butadiene-styrene polymers andcopolymers and blends thereof.
 8. The film composite according to claim6, Wherein said particulates in the image receptive layer are selectedfrom the group consisting of amorphous silica, crystalline silica,calcium carbonate, alumina trihydrate, polyolefin particulates, clays,aluminum silicates and mixtures thereof.
 9. A film composite accordingto claim 1, 2, 3, 4 or 5, wherein the electronically conductive layerpossesses a surface resistivity of 1×10² to 1×10⁸ ohms/sq.
 10. The filmcomposite according to claim 9, wherein the polymer binder for theelectronically conductive particulate is selected from the groupconsisting of copolymers of methyl methacrylate-hydroxyethylmethacrylate, polyester resins, acrylic resins, vinyl chloride resins,vinyl acetate resins, melamine-formaldehyde resin, andphenol-formaldehyde resins.
 11. The film composite according to claim 9,wherein the electronically conductive particulate is:tin oxide dopedwith antimony, phosphorus, indium or fluorine; indium oxide doped withantimony, phosphorus or fluorine; zinc oxide doped with antimony,phosphorus, indium or fluorine; cuprous iodide or silver iodide.
 12. Thefilm composite according to claim 9, wherein the electronicallyconductive particulate is a titanium dioxide, silica or zinc oxidenucleus covered with an antimony doped tin oxide.
 13. The film compositeaccording to claim 9, wherein the electronically conductive particulateis a titanium dioxide, silica or zinc oxide nucleus covered with anfluorine doped tin oxide.
 14. The film composite according to claim 9,wherein the electronically conductive particulate is tin oxide dopedwith antimony, indium, fluorine or phosphorus.
 15. The film compositeaccording to claim 9, wherein the electronically conductive particulateis tin oxide doped with antimony.
 16. The film composite according toclaim 9, wherein the electronically conductive particulate is tin oxidedoped with fluorine.
 17. The film composite according to claim 1, 2, 3,4 or 5, wherein the supporting layer is a transparent or opaquepolyethylene terephthalate, polyolefin, polystyrene, polycarbonate orcellulose acetate.
 18. The film composite according to claim 2, whereinthe transport-assisting layer comprises polymer binders, conductiveagents and particulates, said transport-assisting layer having acoefficient of static and dynamic friction in the range of 0.25 to 0.75and 0.20 to 0.70 units, respectively, and a surface roughness of 10 to100 .[.cc of air/minute.]. .Iadd.Sheffield Units .Iaddend.and a surfaceresistivity of 1×10⁶ to 1×10¹³ ohms/sq. at 25° C. and 50% RH.
 19. Thefilm composite according to claim 18, wherein said polymer binders inthe transport-assisting layer are selected from the group consisting ofhydrolyzed polyvinyl acetate resins, melamine-formaldehyde resins,cellulose acetate propionate resins and cellulose acetate butyrateresins.
 20. The film composite according to claim 18, wherein saidconductive agents in the transport-assisting layer are selected from thegroup consisting of doped metal oxides, quaternary salts of diacetoneacrylamide copolymer resins and sulfonated polystyrene resins.
 21. Thefilm composite according to claim 18, wherein said particulates in thetransport-assisting layer are selected from the group consisting ofsilica and calcium carbonate.
 22. A film composite according to claim 2,wherein the image receptive layer comprises amorphous silica,crystalline silica and calcium carbonate particulates dispersed in apolymer matrix of polyvinyl butyral and polyacrylate;the electronicallyconductive layer comprises a copolymer of methylmethacrylate-hydroxyethyl methacrylate and antimony doped tin oxideparticles; the supporting layer is a clear polyethylene terephthalatefilm, and the transport assisting layer on the side opposite to theimaging side contains silica particulates and polymeric binders.
 23. Afilm composite according to claim 22, wherein the polymeric binders ofthe transport assisting layer are selected from the group consisting ofmelamine-formaldehyde resins, partially hydrolyzed polyvinyl acetateresins and quaternary salts of acrylamide copolymers.
 24. A filmcomposite according to claim 1, 2, 3, 4, 5 or 22, wherein the compositeis transparent and possesses a haze value of from 10 to 45 percent. 25.A film composite according to claim 1, wherein the surface abrasivity ofthe image receptive layer is from 0.03 to 0.07 inch and the surfaceroughness is from 60 to 150 .[.cc of air/minute.]. .Iadd.SheffieldUnits.Iaddend..
 26. A film composite according to claim 22, wherein thesurface abrasivity of the image receptive layer is from 0.03 to 0.07inch and the surface roughness is from 60 to 150 .[.cc of air/minute.]..Iadd.Sheffield Units.Iaddend..
 27. A system for producing anelectrostatic hardcopy print, the system comprising:a writing headhaving a plurality of styli, a backplate or frontplate electrode, meansfor placing electronic charges in latent image form on a recordingmedium, means for applying toner particles to said recording medium, andmeans for fixing the image on the recording medium, said recordingmedium comprising:an image receptive layer having a surface abrasivityof 0.015 inch to 0.085 inch, and a surface roughness of 30 to 180 .[.ccof air/minute.]. .Iadd.Sheffield Units.Iaddend.; an electronicallyconductive layer containing a least one electronically conductiveparticulate in a polymer binder; and a supporting layer, said imagereceptive layer being disposed on said electronically conductive layerwhich is, in turn, disposed on said supporting layer.
 28. A systemaccording to claim 27, further comprising a transport-assisting layer onthe side opposite to the imaging side of the film.
 29. A systemaccording to claim 27, wherein the electronically conductive particulateis a doped metal oxide.
 30. A system according to claim 27, wherein theelectronically conductive particulate is a metal halide.
 31. A systemaccording to claim 27, wherein the electronically conductive particulatecomprises a nucleus which is covered by a conductive metal oxide.
 32. Asystem according to claim 27, wherein the image receptive layer containspolymer binders and particulates, and possesses a dielectric constant of1.5 to 6.5 measured at 25° C. and 1 KHz.
 33. A system according to claim27, wherein the electronically conductive layer possesses a surfaceresistivity of 1×10² to 1×10⁸ ohms/sq.
 34. A system according to claim27, wherein the surface abrasivity of the image receptive layer is from0.03 to 0.07 inch and the surface roughness is from 60 to 150 .[.cc ofair/minute.]. .Iadd.Sheffield Units.Iaddend..